Re: [Xen-devel] [PATCH v11 01/17] libxl: fix stubdom console destruction

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-07-24 at 11:54 +0100, Roger Pau Monne wrote:
> Stefano Stabellini wrote:
> > On Tue, 24 Jul 2012, Roger Pau Monne wrote:
> >> Ian Campbell wrote:
> >>> On Mon, 2012-07-23 at 18:27 +0100, Roger Pau Monne wrote:
> >>>> Stubdoms have several consoles attached, and they don't follow the
> >>>> xenstore protocol for devices, since they are always in state 1. We
> >>>> have to add an exception to libxl__initiate_device_remove, so libxl
> >>>> doesn't wait for them to reach state 6 (Closed).
> >>>>
> >>>> Report: http://markmail.org/message/yqgppcsdip6tnmh6
> >>>>
> >>>> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> >>>> Reported-by: Ian Campbell <ian.campbell@xxxxxxxxxxxxx>
> >>>> Signed-off-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> >>>> ---
> >>>>  tools/libxl/libxl_device.c |    6 ++++--
> >>>>  1 files changed, 4 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
> >>>> index a94beab..c4392fa 100644
> >>>> --- a/tools/libxl/libxl_device.c
> >>>> +++ b/tools/libxl/libxl_device.c
> >>>> @@ -592,8 +592,10 @@ void libxl__initiate_device_remove(libxl__egc *egc,
> >>>>          LOG(ERROR, "unable to get info for domain %d", domid);
> >>>>          goto out;
> >>>>      }
> >>>> -    if (QEMU_BACKEND(aodev->dev) &&
> >>>> -        (info.paused || info.dying || info.shutdown)) {
> >>>> +    if ((QEMU_BACKEND(aodev->dev) &&
> >>>> +        (info.paused || info.dying || info.shutdown)) ||
> >>>> +        (libxl_is_stubdom(CTX, aodev->dev->domid, NULL) &&
> >>>> +        (aodev->dev->backend_kind == LIBXL__DEVICE_KIND_CONSOLE))) {
> >>> Is this actually specific to stubdom consoles or is that just where
> >>> we've noticed it?
> >> It's just that I've noticed it with stubdoms, which AFAIK are the only
> >> domains that can have more than one console.
> > 
> > Linux can handle multiple PV consoles
> 
> But there's no way to create a domain from xl with multiple consoles, or
> at least I haven't been able to find any.

I think it's more theoretically possible at this stage, but we'll
probably add it at some point.

> 
> > 
> >>> Does it apply to LIBXL__CONSOLE_BACKEND_IOEMU as well
> >>> as ..._XENCONSOLED? I took a look through tools/console and I cannot
> >>> find any handling of a state node in xenstore at all, so the XENCONSOLED
> >>> case seems clear. I notice that xen_console.c registers the device with
> >>> DEVOPS_FLAG_IGNORE_STATE but that only seems to affect startup not
> >>> teardown. I don't see a qemu_chr_close (or anything similar) anywhere in
> >>> hw/xen_console.c
> >> So it should apply to any console device? This means I don't have to
> >> wait for any device of type LIBXL__DEVICE_KIND_CONSOLE, and there's no
> >> need to check for the specific console type or Qemu.
> > 
> > xen_console registers a disconnect handler, con_disconnect, that should
> > be able to unbind the evtchn and unmap the ring.
> > "disconnect" is called by xen_backend, if the backend and frontend
> > states are 5 or 6.
> 
> Yes, but I don't see that con_disconnect sets the state to 6 after doing
> the cleanup, neither xenconsoled does so. I think con_disconnect should
> set xendev->be_state = 6, so the parent function xen_be_disconnect would
> notice the state change and write it to xenstore.
> 

The caller in xen_backend.c does this.

> Also, this only happens when a domain has multiple consoles, since the
> first console is a special case and is processed separately, but the
> rest of consoles are processed using the "normal" unplug mechanism
> (libxl__initiate_device_remove). Maybe we should treat all consoles in
> the same way, and unplug them using the same method that we use for the
> first console?
> 
> There's a comment before destroying the first console that states:
> 
> /* Currently console devices can be destroyed synchronously by just
>  * removing xenstore entries, this is what libxl__device_destroy does.
>  */
> libxl__device_destroy(gc, dev);
> 
> It makes me think if the appropriate solution would be to call
> libxl__device_destroy for all console devices, not only for the first one.



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